1. Field of Invention
The present invention relates to a linear guiding mechanism. More particularly, the present invention relates to a linear guiding mechanism for guiding horizontal movement of the carrier chassis of an optical scanner.
2. Description of Related Art
As computing power, network and multi-media technologies continue to improve, the optical scanner has become an indispensable piece of equipment for capturing text or picture images and converting them into a digital image file. Maturity of techniques for fabricating the optical scanner also brings about widespread use alongside a personal computer. At present, the most common type of optical scanner is the platform scanner. In general, a platform scanner includes a transparent flat panel for placing a document or image to be scanned. Through an internal optical system inside the scanner, the analogue image on the document or image is scanned to produce corresponding digital signals. The digital signals are gathered to produce an image file so that the image file may be displayed, identified, edited, stored or transmitted thereafter.
The optical system of a platform scanner comprises a light source, a lens, a reflecting mirror and an optical or optical-electrical sensor such as a charge-coupled device (CCD) sensor all enclosed within an carrier chassis. Since the optical sensor is a one-dimensional device without any movement, movement in a second dimension has to be introduced in order to scan the entire document or picture image. Hence, a conventional platform scanner has a transmission assembly for driving the carrier chassis horizontally in a straight line so that each segment within the document or image is brought under the optical sensor.
To explain the linear driving mechanism of the carrier chassis within a platform scanner, refer to FIGS. 1A and 1B. FIGS. 1A and 1B are the respective front view and top view of the carrier chassis of a conventional platform scanner and associated driving assembly. The carrier chassis 122 of an optical system 120 is installed over a scanner housing 110 (only a portion of the entire structure is shown). To drive both ends of the carrier chassis in the forward direction and back as indicated, the stepper motor 136 of a driving system 130 drives, directly or indirectly by means of a belt wheel 134a, a belt 132 wrapped around the belt wheel 134a and another belt wheel 134b. In the meantime, the clamping structure 124 on the carrier chassis 122 clamps onto a section of the driving belt 132. In addition, an axial sheath 126 on the carrier chassis 122 is slid onto a positioning rod 140. With this arrangement, the carrier chassis 122 can move horizontally forward and backward in a linear direction along the longitudinal direction of the positioning rod 140 when driven by the belt 132.
Due to width requirement of scanning, the carrier chassis 122 has a fixed structural length so that both ends of the carrier chassis 122 may move horizontally in the indicated directions. A conventional platform scanner utilizes the driving system 130 (such as the right side as shown in FIG. 1B) to drive one end of the carrier chassis 122 and the axial sheath 126 around the axial rod 140 to serve as a guide in the motion. In addition, a passively driven wheel 128 is fixed to the bottom section on the other end of the carrier chassis 122 (on the left side as shown in FIG. 1A). Hence, both ends of the carrier chassis 122 may move synchronously and smoothly forward or backward along the axial rod 140 direction on a horizontal plane.
In brief, a conventional platform scanner uses an axial sheath on a carrier chassis and a corresponding axial rod to serve as a linear guiding mechanism so that the carrier chassis is able to move in the axial rod direction when driven by a driving system. Note, however, that most conventional platform scanners are assembled such that the positioning rod must be precisely assembled to the scanner housing. In addition, most positioning rods must be made from metal. Since a metallic rod generally has a higher procurement cost, overall production cost of the platform scanner is increased